The field of the invention is interface materials in electronic component and layered materials applications.
Electronic components are used in ever increasing numbers of consumer and commercial electronic products. Examples of some of these consumer and commercial products are televisions, personal computers, internet servers, cell phones, pagers, handheld electronic organizers, portable radios, car stereos, or remote controls. As the demand for these consumer and commercial electronics increases, there is also a demand for those same products to become smaller, more functional, and more portable for consumers and businesses.
As a result of the size decrease in these products, the components that comprise the products must also become smaller. Examples of some of those components that need to be reduced in size or scaled down are printed circuit or wiring boards, resistors, wiring, keyboards, touch pads, and chip packaging.
Components, therefore, are being broken down and investigated to determine if there are better building materials and methods that will allow them to be scaled down to accommodate the demands for smaller electronic components. In layered components, one goal appears to be decreasing the number of the layers while at the same time increasing the functionality and durability of the remaining layers. This task can be difficult, however, given that several of the layers and components of the layers should generally be present in order to operate the device.
Also, as electronic devices become smaller and operate at higher speeds, energy emitted in the form of heat increases dramatically. A popular practice in the industry is to use thermal grease, or grease-like materials, alone or on a carrier in such devices to transfer the excess heat dissipated across physical interfaces. Most common types of thermal interface materials are thermal greases, phase change materials, and elastomer tapes. Thermal greases or phase change materials have lower thermal resistance than elastomer tape because of the ability to be spread in very thin layers and provide intimate contact between adjacent surfaces. Typical thermal impedance values range between 0.6-1.6xc2x0 C. cm2/w. However, a serious drawback of thermal grease is that thermal performance deteriorates significantly after thermal cycling, such as from 65xc2x0 C. to 150xc2x0 C., or after power cycling when used in VLSI chips. It has also been found that the performance of these materials deteriorates when large deviations from surface planarity causes gaps to form between the mating surfaces in the electronic devices or when large gaps between mating surfaces are present for other reasons, such as manufacturing tolerances, etc. When the heat transferability of these materials breaks down, the performance of the electronic device in which they are used is adversely affected.
Thus, there is a continuing need to: a) design and produce thermal interface materials and layered materials that meet customer specifications while minimizing the size of the device and number of layers; b) develop reliable methods of producing desired thermal interface materials and layered materials and components comprising contemplated thermal interface and layered materials; and c) develop and implement methods of applying the desired thermal interface materials and layered materials and components comprising contemplated thermal interface and layered materials.
A contemplated crosslinkable thermal interface material is produced by combining at least one rubber compound, at least one amine resin and at least one thermally conductive filler. This contemplated interface material takes on the form of a liquid or xe2x80x9csoft gelxe2x80x9d. The gel state is brought about through a crosslinking reaction between the at least one rubber compound composition and the at least one amine resin composition. More specifically, the amine resin is incorporated into the rubber composition to crosslink the primary hydroxyl groups on the rubber compounds thus forming the soft gel phase. Therefore, it is contemplated that at least some of the rubber compounds will comprise at least one terminal hydroxyl group.
Amine or amine-based resins are added or incorporated into the rubber composition or mixture of rubber compounds primarily to facilitate a crosslinking reaction between the amine resin and the primary or terminal hydroxyl groups on at least one of the rubber compounds. The crosslinking reaction between the amine resin and the rubber compounds leads to a xe2x80x9csoft gelxe2x80x9d phase or paste phase to the mixture, instead of a liquid state.
Once the foundation composition that comprises at least one rubber compound, at least one amine resin, and at least one thermally conductive filler has been prepared, the composition must be compared to the needs of the electronic component, vendor, or electronic product to determine whether a phase change material is needed to change some of the physical properties of the composition.
Phase change materials are useful in thermal interface material applications because they store and release heat as they oscillate between solid and liquid form. A phase change material gives off heat as it changes to a solid state, and as it returns to a liquid, it absorbs heat. The phase change temperature is the melting temperature at which the heat absorption and rejection takes place.
A method for forming the crosslinkable thermal interface materials disclosed herein comprises a) providing at least one saturated rubber compound, b) providing at least one amine resin, c) crosslinking the at least one saturated rubber compound and the at least one amine resin to form a crosslinked rubber-resin mixture, d) adding at least one thermally conductive filler to the crosslinked rubber-resin mixture, and e) adding a wetting agent to the crosslinked rubber-resin mixture. This method can also further comprise adding at least one phase change material to the crosslinked rubber-resin mixture and/or adding at least one solvent or additional solvent to the crosslinked rubber-resin mixture or the crosslinked rubber-resin and phase change material mixture, in order to facilitate formation of the mixture into a paste and also in order to facilitate application of the mixture to a surface or substrate.
The contemplated thermal interface material can be provided as a dispensable liquid paste to be applied by dispensing methods, such as by screen printing, ink jet printing, thread dispensing; spraying; stamping; all types of lithography or wet offset; roller printing; letter press printing; gravure printing; flexographic printing; planographic printing; offset printing; mimeo graphic printing; thermography; hot stamping and transfer printing techniques; as well as brushing and stenciling techniques. In short, any printing or dispensing process that can incorporate a paste and/or soft gel product or material can be employed effectively with embodiments of the present teachings. The dispensable liquid paste can then be cured as desired.
Contemplated thermal interface materials can also be provided as a highly compliant, cured, elastomer film or sheet for pre-application on interface surfaces, such as heat sinks. It can further be provided and produced as a soft gel or liquid that can be applied to surfaces by any suitable dispensing method, including those previously mentioned. Even further, the material can be provided as a tape that can be applied directly to interface surfaces or electronic components.
Applications of the contemplated thermal interface materials described herein comprise incorporating the materials into a layered material, an electronic component or a finished electronic product.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention.